HEAT-TRANSFER AND PRESSURE-DROP CORRELATIONS FOR TWISTED-TAPE INSERTSIN ISOTHERMAL TUBES .2. TRANSITION AND TURBULENT FLOWS

Thermal-hydraulic design correlations are developed to predict isother mal f and Nu for in-tube, turbulent flows with twisted-tape inserts. E xperimental data taken for water and ethylene glycol, with y = 3.0, 4. 5, and 6.0, are analyzed, and various mechanisms attributed to twisted tapes are identified. Tube blockage and tape-induced vortex mixing ar e the dominant phenomena that result in increased heat transfer and pr essure drop; for loose- to snug-fitting tapes, the fin effects are ins ignificant. The limiting case of a straight tape insert correlates wit h the hydraulic-diameter-based smooth tube equation. Tape twist effect s are thus isolated by normalizing the data with the asymptotic predic tions for y = infinity, and the swirl effects are found to correlate w ith Re and l/y. The validity of the final correlations is verified by comparing the predictions with previously published data, which includ e both gases and liquids, under heating and cooling conditions and a w ide range of tape geometries, thereby establishing a very generalized applicability. Finally, correlations for laminar (presented in the com panion Part I paper) and turbulent flows are combined into single, con tinuous equations. For isothermal f, the correlation describes most of the available data for laminar-transition-turbulent flows within +/- 10 percent. For Nu, however, a family of curves is needed due to the n onunique nature of laminar-turbulent transition.